In order to optimize yarn processing performance and end-product quality, tests are commonly applied to textile entities which include fibers and undesirable entities such as neps and trash. Zellweger Uster, Inc., Knoxville, Tenn.; Uster, Switzerland; and others manufacture a wide range of fiber and yarn testing instruments, both of the laboratory type and the on-line process control type, that are increasingly used by textile producers worldwide.
In today's highly competitive and quality conscious marketplace the use of these instruments in laboratory testing and process monitoring has gone beyond simply giving the user a competitive advantage. Their use has, in the area of classing cotton for loan eligibility, been dictated by the U.S. government, and has otherwise become a requirement of business survival. Raw materials are procured and lots of finished goods are accepted or rejected based on fiber and yarn properties as determined by these instruments. For example, nearly 100% of U.S. cotton bales are classified as to fiber length, fiber strength/elongation, color, micronaire, and trash content by HVI (High Volume Instrumentation) systems (manufactured by Zellweger Uster, Inc., Knoxville, Tenn.), thus replacing the traditional human cotton classer. The measured results determine the monetary value of the bale and serve as a first process control measurement for spinning mills.
Increased demands on fiber properties, such as increased fiber cleanliness and decreased neps and short fiber content, have brought increased demands for instruments that measure those properties and increased expectations for the precision and accuracy of the measurements. For instance, the AFIS (Advanced Fiber Information System), also manufactured by Zellweger Uster, Inc., Knoxville, Tenn. and described in the papers "Utilization of the Complete Fiber Length Distribution from the Advanced Fiber Information System" and "Electro-Optical Trash Particle Counting and Sizing", Bremen Cotton Conference, Bremen, Germany, and in various copending patent applications referenced hereinbelow, can make measurements of fiber trash content, fiber length distributions (including short fiber content), and fiber nep levels. MANTIS, also manufactured by Zellweger Uster, Knoxville, Tenn., can measure single fiber breaking tension, elongation, and diameters. MANTIS is described in U.S. Pat. No. 5,138,879.
Both instrument and process machinery manufacturers have long known that the microenvironment surrounding the test or processing zones can have a profound effect on fiber measurement and processing performance parameters. For example, cotton fiber is mostly cellulose and is highly hygroscopic. Increasing moisture content increases strength, causes fiber swelling, aggravates cleaning and sugar-related "stickiness", and reduces electro-static effects. These and other changes in fiber behavior associated with the test or processing micro-environment are well known and are utilized to a limited extent by textile fiber processors by controlling the macroenvironment. In ginning, for example, moisture content in the fiber is purposefully reduced to about 5% or below by driers. This allows more effective cleaning but, along with other effects, weakens the fibers and aggravates static charge problems. On the other hand, in weaving rooms where fiber and associated yarn strength is critical, the relative humidity may be held as high as 85%, corresponding to a moisture content of about 9% in the yarn.
However, precise macroenvironmental control in testing laboratories or manufacturing facilities is difficult, expensive and, in most cases, far less effective than desired. A large controlled space offers a buffer to small perturbations in, for example, humidity, temperature, and ion concentration, but is slow to respond to control actions. It is common to find very expensive (millions of dollars for large production areas) macroenvironmental control systems which, indeed, control relative humidity and temperature to .+-.2%, and .+-.1.degree. F. but, unfortunately, allow the test or production zone to fluctuate .+-.10% and .+-.5.degree. F.
As discussed in Shofner U.S. Pat. Nos. 4,512,060, 4,631,781 and 4,686,744, increasing demands are being placed on fiber properties as textile processing machinery production rates increase and as the tolerances of textile processing machinery for variances in the fiber properties decrease. Current production and harvesting methods inherently entrain more foreign matter content into cotton fiber, for example, such that the ginning and cleaning actions required to achieve a given percentage of foreign matter content are increasing. Increased cleaning is always at the expense of fiber loss and damage. The incompatibility between the goals of clean versus undamaged fiber increases the difficulties faced by producer, ginner, merchant and spinner. Providing clean and undamaged fiber is a major, world-wide problem and improved processing methods and apparatus are urgently needed, especially in the areas of test zone and process zone environmental control.
As generally recognized in the above-identified Shofner U.S. Pat. Nos. 4,512,062, 4,631,701 and 4,686,744, it is advantageous to condition air or other gas, such as transport gas, in both processing and testing machines for improved machine operation. For example, as disclosed in those patents, there can be a preferred state of the fiber with regard to humidity and static charge for a particular operation, such as a cleaning operation. It is further recognized in those patents that parameters such as humidity and electrostatic charge of the fiber may be different at each of a plurality of different processing stages. Although temperature, humidity and static charge are perhaps the most obvious parameters of transport gas which may be conditioned, others are possible. For example, the above-identified patents also disclose the conditioning of transport gas as to humidity, temperature, pressure, gas composition, free charge concentration, static charge, radioactive particle concentration, velocity and pressure fluctuations.
Other examples of controlling temperature and humidity in particular in a textile processing machine are disclosed in Thannheiser U.S. Pat. No. 4,527,306 and Leifeld et al U.S. Pat. No. 5,121,522. Those patents describe systems in which pneumatic transport air within a textile processing machine is conditioned with respect to temperature and humidity, employing a feedback control system. U.S. Pat. No. 5,121,522 in particular discloses a system for measuring "humidity" and temperature of fiber tufts directly for use in controlling an air conditioning system. As noted in those patents, one reason for control is that if, for example, the transport air is too dry, electrostatic charges can cause undesirable fiber accumulations within the equipment. On the other hand, if the transport air is too humid, balling of fiber tufts can result.
Thus, the control of moisture content in fiber processing is well known. Further, under the influence of conditioned gas flow, it is known that single fibers can reach a point of equilibrium (e.g. with respect to moisture content) almost instantaneously, whereas tufts or masses of fibers require longer periods of time to reach equilibrium.
There are, however, a number of conflicting considerations, which have not heretofore been effectively addressed. It is known, for example, that fiber is best cleaned when fiber moisture content is relatively low, for example, below 5%. It is also known that the strength of cotton fiber is a maximum at a relatively higher moisture content, for example, above 5%. Strength of cotton fiber affects the degree of undesirable fiber breakage during processing operations.